Effect of exoskeletal joint constraint and passive resistance on metabolic energy expenditure: Implications for walking in paraplegia

Abstract

An important consideration in the design of a practical system to restore walking in individuals with spinal cord injury is to minimize metabolic energy demand on the user. In this study, the effects of exoskeletal constraints on metabolic energy expenditure were evaluated in able-bodied volunteers to gain insight into the demands of walking with a hybrid neuroprosthesis after paralysis. The exoskeleton had a hydraulic mechanism to reciprocally couple hip flexion and extension, unlocked hydraulic stance controlled knee mechanisms, and ankles fixed at neutral by ankle-foot orthoses. These mechanisms added passive resistance to the hip (15 Nm) and knee (6 Nm) joints while the exoskeleton constrained joint motion to the sagittal plane. The average oxygen consumption when walking with the exoskeleton was 22.5 ± 3.4 ml O2/min/kg as compared to 11.7 ± 2.0 ml O2/min/kg when walking without the exoskeleton at a comparable speed. The heart rate and physiological cost index with the exoskeleton were at least 30% and 4.3 times higher, respectively, than walking without it. The maximum average speed achieved with the exoskeleton was 1.2 ± 0.2 m/s, at a cadence of 104 ± 11 steps/min, and step length of 70 ± 7 cm. Average peak hip joint angles (25 ± 7°) were within normal range, while average peak knee joint angles (40 ± 8°) were less than normal. Both hip and knee angular velocities were reduced with the exoskeleton as compared to normal. While the walking speed achieved with the exoskeleton could be sufficient for community ambulation, metabolic energy expenditure was significantly increased and unsustainable for such activities. This suggests that passive resistance, constraining leg motion to the sagittal plane, reciprocally coupling the hip joints, and weight of exoskeleton place considerable limitations on the utility of the device and need to be minimized in future designs of practical hybrid neuroprostheses for walking after paraplegia.

The Effects of Powered Exoskeleton Gait Training on Cardiovascular Function and Gait Performance: A Systematic Review

“…The design of the selected studies included case series/reports ( n = 7) [ 34 , 35 , 36 , 41 , 42 , 44 , 47 ], pilot studies ( n = 1) [ 28 ], prospective open label ( n = 1) [ 39 ], self-controlled feasibility ( n = 1) [ 31 ], longitudinal cohort ( n = 1) [ 40 ], prospective cohort ( n = 1) [ 38 ], randomised crossover trial ( n = 2) [ 37 , 43 ], open label prospective quasi-experimental ( n = 1) [ 30 ], prospective single group observational ( n = 1) [ 14 ], experimental ( n = 5) [ 22 , 29 , 32 , 33 , 45 ], cross sectional ( n = 1) [ 21 ] and comparative ( n = 1) [ 46 ] studies. The studies were conducted in the USA ( n = 13) [ 14 , 22 , 28 , 32 , 34 , 35 , 37 , 39 , 40 , 41 , 42 , 44 , 45 ], UK ( n = 2) [ 29 , 31 ], Canada ( n = 2) [ 21 , 38 ], Korea ( n = 2) [ 36 , 43 ], Italy ( n = 2) [ 33 , 47 ] and Australia ( n = 1) [ …”

Supplemental Stimulation Improves Swing Phase Kinematics During Exoskeleton Assisted Gait of SCI Subjects With Severe Muscle Spasticity

“…Depending primarily on FES alone for gait can be metabolically taxing, is prone to rapid fatigue, and may lack limb control and stability. For these reasons effort has gone into combining FES with orthotic devices, generally called hybrid FES systems, which can provide several advantages relative to using FES alone (Andrews et al, 1988 ; Isakov et al, 1992 ; Goldfarb et al, 2003 ; Bulea et al, 2013 ; del-Ama et al, 2014 ; Chang et al, 2017 ; Anaya et al, 2018 ), and one prior study investigated a hybrid FES system that couples FES with a robotic exoskeleton (Ha et al, 2016 ). That study specifically coupled a lower limb exoskeleton with FES of the quadriceps and hamstrings muscle groups of each leg, and demonstrated reduced exoskeleton motor torque and power when used in a hybrid FES manner.…”

A Muscle-First, Electromechanical Hybrid Gait Restoration System in People With Spinal Cord Injury

“…With that design, able bodied users were able to achieve gait speeds of 1.2 m/s. This required peak joint velocities of 142 deg/s at the hip joint, and 328 deg/s at the knee joint (Chang et al, 2017 ). A goal of the current work was to develop joints for the exoskeleton that improved upon the passive resistance performance of that prior design while achieving similar joint angular velocities.…”

“…The system's passive resistance and the inability of the exoskeleton to add power were noted as limiting factors. It's capacity to support high speed gait (>1 m/s) was demonstrated with able body participants, although the metabolic cost to do so was high (Chang et al, 2017 ).…”